Internet Engineering Task Force (IETF) R. Housley
Request for Comments: 5934 Vigil Security, LLC
Category: Standards Track S. Ashmore
ISSN: 2070-1721 National Security Agency
C. Wallace
Cygnacom Solutions
August 2010
Trust Anchor Management Protocol (TAMP)
Abstract
This document describes a transport independent protocol for the
management of trust anchors (TAs) and community identifiers stored in
a trust anchor store. The protocol makes use of the Cryptographic
Message Syntax (CMS), and a digital signature is used to provide
integrity protection and data origin authentication. The protocol
can be used to manage trust anchor stores containing trust anchors
represented as Certificate, TBSCertificate, or TrustAnchorInfo
objects.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5934.
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RFC 5934 TAMP August 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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RFC 5934 TAMP August 2010
This specification does not provide for confidentiality of TAMP
messages. If confidentiality is required, then the communications
environment that is used to transfer TAMP messages must provide it.
This specification is intended to satisfy the protocol-related
requirements expressed in "Trust Anchor Management Requirements"
[TA-MGMT-REQS] and uses vocabulary from that document.
TAMP messages may be exchanged in real time over a network, such as
via HTTP as described in Appendix A, or may be stored and transferred
using other means. TAMP exchanges consist of a request message that
includes instructions for a trust anchor store and, optionally, a
corresponding response message that reports the result of carrying
out the instructions in the request. Response messages need not be
propagated in all cases. For example, a GPS receiver may be unable
to transmit a response and may instead use an attached display to
indicate the results of processing a TAMP request.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Trust Anchors
TAMP manages trust anchors. A trust anchor contains a public key
that is used to validate digital signatures. TAMP recognizes three
formats for representing trust anchor information: Certificate
[RFC5280], TBSCertificate [RFC5280], and TrustAnchorInfo [RFC5914].
All trust anchors are distinguished by the public key, and all trust
anchors consist of the following components:
o A public key signature algorithm identifier and associated public
key, which MAY include parameters
o A public key identifier
Other information may appear in a trust anchor, including
certification path processing controls and a human readable name.
TAMP recognizes three types of trust anchors based on functionality:
apex trust anchors, management trust anchors, and identity trust
anchors.
In addition to the information described above, apex trust anchors
and management trust anchors that sign TAMP messages have an
associated sequence number that is used for replay detection.
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RFC 5934 TAMP August 2010
The public key is used to name a trust anchor, and the public key
identifier is used to identify the trust anchor as a signer of a
particular object, such as a SignedData object or a public key
certificate. This public key identifier can be stored with the trust
anchor, or in most public key identifier assignment methods, it can
be computed from the public key whenever needed.
A trust anchor public key can be used in two different ways to
support digital signature validation. In the first approach, the
trust anchor public key is used directly to validate the digital
signature. In the second approach, the trust anchor public key is
used to validate an X.509 certification path, and then the subject
public key in the final certificate in the certification path is used
to validate the digital signature. When the second approach is
employed, the certified public key may be used for things other than
digital signature validation; the other possible actions are
constrained by the key usage certificate extension.
TAMP implementations MUST support validation of TAMP messages that
are directly validated using a trust anchor. Support for TAMP
messages validated using an X.509 certificate validated using a trust
anchor, or using longer certification paths, is OPTIONAL. The CMS
provides a location to carry X.509 certificates, and this facility
can be used to transfer certificates to aid in the construction of
the certification path.
1.2.1. Apex Trust Anchors
Within the context of a single trust anchor store, one trust anchor
is superior to all others. This trust anchor is referred to as the
apex trust anchor. This trust anchor represents the ultimate
authority over the trust anchor store. Much of this authority can be
delegated to other trust anchors.
The apex trust anchor private key is expected to be controlled by an
entity with information assurance responsibility for the trust anchor
store. The apex trust anchor is by definition unconstrained and
therefore does not have explicit authorization information associated
with it.
Due to the special nature of the apex trust anchor, TAMP includes
separate facilities to change it. In particular, TAMP includes a
facility to securely replace the apex trust anchor. This action
might be taken for one or more of the following reasons:
o The crypto period for the apex trust anchor public/private key
pair has come to an end
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RFC 5934 TAMP August 2010
o The apex trust anchor private key is no longer available
o The apex trust anchor public/private key pair needs to be revoked
o The authority has decided to use a different digital signature
algorithm or the same digital signature algorithm with different
parameters, such as a different elliptic curve
o The authority has decided to use a different key size
o The authority has decided to transfer control to another authority
To accommodate these requirements, the apex trust anchor MAY include
two public keys. Whenever the apex trust anchor is updated, both
public keys will be replaced. The first public key, called the
operational public key, is used in the same manner as other trust
anchors. Any type of TAMP message, including an Apex Trust Anchor
Update message, can be validated with the operational public key.
The second public key, called the contingency public key, can only be
used to update the apex trust anchor. The contingency private key
SHOULD be used at only one point in time; it is used only to sign an
Apex Trust Anchor Update message that results in its own replacement
(as well as the replacement of the operational public key). The
contingency public key is distributed in encrypted form. When the
contingency public key is used to validate an Apex Trust Anchor
Update message, the symmetric key needed to decrypt the contingency
public key is provided as part of the signed Apex Trust Anchor Update
message that is to be verified with the contingency public key.
1.2.2. Management Trust Anchors
Management trust anchors are used in the management of cryptographic
modules. For example, the TAMP messages specified in this document
are validated to a management trust anchor. Likewise, a signed
firmware package as specified in [RFC4108] is validated to a
management trust anchor.
1.2.3. Identity Trust Anchors
Identity trust anchors are used to validate certification paths, and
they represent the trust anchor for a public key infrastructure.
They are most often used in the validation of certificates associated
with non-management applications.
Housley, et al. Standards Track [Page 7]

RFC 5934 TAMP August 20101.3. Architectural Elements
TAMP does not assume any particular architecture. However, TAMP
REQUIRES the following architectural elements: a cryptographic
module, a trust anchor store, TAMP protocol processing, and other
application-specific protocol processing.
A globally unique algorithm identifier MUST be assigned for each one-
way hash function, digital signature generation/validation algorithm,
and symmetric key unwrapping algorithm that is implemented. To
support CMS, an object identifier (OID) is assigned to name a one-way
hash function, and another OID is assigned to name each combination
of a one-way hash function when used with a digital signature
algorithm. Similarly, certificates associate OIDs assigned to public
key algorithms with subject public keys, and certificates make use of
an OID that names both the one-way hash function and the digital
signature algorithm for the certificate issuer digital signature.
[RFC3279], [RFC3370], [RFC5753], and [RFC5754] provide OIDs for a
number of commonly used algorithms; however, OIDs may be defined in
later or different specifications.
1.3.1. Cryptographic Module
The cryptographic module MUST include the following capabilities:
o The cryptographic module SHOULD support the secure storage of a
digital signature private key to sign TAMP responses and either a
certificate containing the associated public key or a certificate
designator. In the latter case, the certificate is stored
elsewhere but is available to parties that need to validate
cryptographic module digital signatures. The designator is a
public key identifier.
o The cryptographic module MUST support at least one one-way hash
function, one digital signature validation algorithm, one digital
signature generation algorithm, and, if contingency keys are
supported, one symmetric key unwrapping algorithm. If only one
one-way hash function is present, it MUST be consistent with the
digital signature validation and digital signature generation
algorithms. If only one digital signature validation algorithm is
present, it MUST be consistent with the apex trust anchor
operational public key. If only one digital signature generation
algorithm is present, it MUST be consistent with the cryptographic
module digital signature private key. These algorithms MUST be
available for processing TAMP messages, including the content
types defined in [RFC5652], and for validation of X.509
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RFC 5934 TAMP August 2010
certification paths. As with similar specifications, such as
RFC 5280, this specification does not mandate support for any
cryptographic algorithms. However, algorithm requirements may be
imposed by specifications that use trust anchors managed via TAMP.
1.3.2. Trust Anchor Store
The trust anchor store MUST include the following capabilities:
o Each trust anchor store MUST have a unique name. For example, a
cryptographic module containing a single trust anchor store may be
identified by a unique serial number with respect to other modules
within the same family where the family is represented as an ASN.1
object identifier (OID) and the unique serial number is
represented as a string of octets. Other means of establishing a
unique name are also possible.
o Each trust anchor store SHOULD have the capability to securely
store one or more community identifiers. The community identifier
is an OID, and it identifies a collection of cryptographic modules
that can be the target of a single TAMP message or the intended
recipients for a particular management message.
o The trust anchor store SHOULD support the use of an apex trust
anchor. If apex support is provided, the trust anchor store MUST
support the secure storage of exactly one apex trust anchor. The
trust anchor store SHOULD support the secure storage of at least
one additional trust anchor. Each trust anchor MUST contain a
unique public key. A public key MUST NOT appear more than once in
a trust anchor store.
o The trust anchor store MUST have the capability to securely store
a sequence number for each trust anchor authorized to generate
TAMP messages and be able to report the sequence number along with
the key identifier of the trust anchor.
1.3.3. TAMP Processing Dependencies
TAMP processing MUST include the following capabilities:
o TAMP processing MUST have a means of locating an appropriate trust
anchor. Two mechanisms are available. The first mechanism is
based on the public key identifier for digital signature
verification, and the second mechanism is based on the trust
anchor X.500 distinguished name and other X.509 certification path
controls for certificate path discovery and validation. The first
mechanism MUST be supported, but the second mechanism MAY be
supported.
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RFC 5934 TAMP August 2010
o TAMP processing MUST be able to invoke the digital signature
validation algorithm using the public key held in secure storage
for trust anchors.
o TAMP processing MUST have read and write access to secure storage
for sequence numbers associated with each TAMP message signer as
described in Section 6.
o TAMP processing MUST have read and write access to secure storage
for trust anchors in order to update them. Update operations
include adding trust anchors, removing trust anchors, and
modifying trust anchors. Application-specific constraints MUST be
securely stored with each management trust anchor as described in
Section 1.3.4.
o TAMP processing MUST have read access to secure storage for the
community membership list, if any, to determine whether a targeted
message ought to be accepted.
o To implement the OPTIONAL community identifier update feature,
TAMP processing MUST have read and write access to secure storage
for the community membership list.
o To generate signed confirmation messages, TAMP processing MUST be
able to invoke the digital signature generation algorithm using
the cryptographic module digital signature private key, and it
MUST have read access to the cryptographic module certificate or
its designator. TAMP uses X.509 certificates [RFC5280].
o The TAMP processing MUST have read access to the trust anchor
store unique name.
1.3.4. Application-Specific Protocol Processing
The apex trust anchor and management trust anchors managed with TAMP
can be used by the TAMP application. Other management applications
MAY make use of all three types of trust anchors, but non-management
applications SHOULD only make use of identity trust anchors.
Applications MUST ensure that usage of a trust anchor is consistent
with any constraints associated with the trust anchor. For example,
if name constraints are associated with a trust anchor, certification
paths that start with the trust anchor and contain certificates with
names that violate the name constraints MUST be rejected.
The application-specific protocol processing MUST be provided with
the following services:
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RFC 5934 TAMP August 2010
o The application-specific protocol processing MUST have a means of
locating an appropriate trust anchor. Two mechanisms are
available to applications. The first mechanism is based on the
public key identifier for digital signature verification, and the
second mechanism is based on the trust anchor X.500 distinguished
name and other X.509 certification path controls for certificate
path discovery and validation.
o The application-specific protocol processing MUST be able to
invoke the digital signature validation algorithm using the public
key held in secure storage for trust anchors.
o The application-specific protocol processing MUST have read access
to data associated with trust anchors to ensure that constraints
can be enforced appropriately. For example, an application MUST
have read access to any name constraints associated with a TA to
ensure that certification paths terminated by that TA do not
include certificates issued to entities outside the TA manager-
designated namespace.
o The application-specific protocol processing MUST have read access
to secure storage for the community membership list, if any, to
determine whether a targeted message ought to be accepted.
o If the application-specific protocol requires digital signatures
on confirmation messages or receipts, then the application-
specific protocol processing MUST be able to invoke the digital
signature generation algorithm with the cryptographic module
digital signature private key and its associated certificate or
certificate designator. Digital signature generation MUST be
controlled in a manner that ensures that the content type of
signed confirmation messages or receipts is appropriate for the
application-specific protocol processing.
o The application-specific protocol processing MUST have read access
to the trust anchor store unique name.
1.4. ASN.1 Encoding
The CMS uses Abstract Syntax Notation One (ASN.1) [X.680]. ASN.1 is
a formal notation used for describing data protocols, regardless of
the programming language used by the implementation. Encoding rules
describe how the values defined in ASN.1 will be represented for
transmission. The Basic Encoding Rules (BER) [X.690] are the most
widely employed rule set, but they offer more than one way to
represent data structures. For example, definite-length encoding and
indefinite-length encoding are supported. This flexibility is not
desirable when digital signatures are used. As a result, the
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RFC 5934 TAMP August 2010
Distinguished Encoding Rules (DER) [X.690] were invented. DER is a
subset of BER that ensures a single way to represent a given value.
For example, DER always employs definite-length encoding.
Digitally signed structures MUST be encoded with DER. In other
specifications, structures that are not digitally signed do not
require DER, but in this specification, DER is REQUIRED for all
structures. By always using DER, the TAMP processor will have fewer
options to implement.
ASN.1 is used throughout the text of this document for illustrative
purposes. The authoritative source of ASN.1 for the structures
defined in this document is Appendix A.
2. Cryptographic Message Syntax Profile
TAMP makes use of signed and unsigned messages. The Cryptographic
Message Syntax (CMS) is used in both cases. A digital signature is
used to protect the message from undetected modification and provide
data origin authentication. TAMP makes no general provision for
encryption of content.
CMS is used to construct a signed TAMP message. The CMS ContentInfo
content type MUST always be present. For signed messages,
ContentInfo MUST encapsulate the CMS SignedData content type; for
unsigned messages, ContentInfo MUST encapsulate the TAMP message
directly. The CMS SignedData content type MUST encapsulate the TAMP
message. A unique content type identifier identifies the particular
type of TAMP message. The CMS encapsulation of a signed TAMP message
is summarized by:
ContentInfo {
contentType id-signedData, -- (1.2.840.113549.1.7.2)
content SignedData
}
SignedData {
version CMSVersion, -- Always set to 3
digestAlgorithms DigestAlgorithmIdentifiers, -- Only one
encapContentInfo EncapsulatedContentInfo,
certificates CertificateSet, -- OPTIONAL signer certificates
crls CertificateRevocationLists, -- OPTIONAL
signerInfos SET OF SignerInfo -- Only one
}
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RFC 5934 TAMP August 2010
SignerInfo {
version CMSVersion, -- Always set to 3
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs SignedAttributes,
-- REQUIRED in TAMP messages
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs UnsignedAttributes -- OPTIONAL; may only be
} -- present in Apex Trust
-- Anchor Update messages
EncapsulatedContentInfo {
eContentType OBJECT IDENTIFIER, -- Names TAMP message type
eContent OCTET STRING -- Contains TAMP message
}
When a TAMP message is used to update the apex trust anchor, this
same structure is used; however, the digital signature will be
validated with either the apex trust anchor operational public key or
the contingency public key. When the contingency public key is used,
the symmetric key needed to decrypt the previously stored contingency
public key is provided as a contingency-public-key-decrypt-key
unsigned attribute. Section 4.5 of this document describes the Apex
Trust Anchor Update message.
CMS is also used to construct an unsigned TAMP message. The CMS
ContentInfo structure MUST always be present, and it MUST be the
outermost layer of encapsulation. A unique content type identifier
identifies the particular TAMP message. The CMS encapsulation of an
unsigned TAMP message is summarized by:
ContentInfo {
contentType OBJECT IDENTIFIER, -- Names TAMP message type
content OCTET STRING -- Contains TAMP message
}
2.1. ContentInfo
CMS requires the outermost encapsulation to be ContentInfo [RFC5652].
The fields of ContentInfo are used as follows:
o contentType indicates the type of the associated content, and for
TAMP, the encapsulated type is either SignedData or the content
type identifier associated with an unsigned TAMP message. When
the id-signedData (1.2.840.113549.1.7.2) object identifier is
present in this field, then a signed TAMP message is in the
content. Otherwise, an unsigned TAMP message is in the content.
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RFC 5934 TAMP August 2010
o content holds the content, and for TAMP, the content is either a
SignedData content or an unsigned TAMP message.
2.2. SignedData Info
The SignedData content type [RFC5652] contains the signed TAMP
message and a digital signature value; the SignedData content type
MAY also contain the certificates needed to validate the digital
signature. The fields of SignedData are used as follows:
o version is the syntax version number, and for TAMP, the version
number MUST be set to 3.
o digestAlgorithms is a collection of one-way hash function
identifiers, and for TAMP, it contains a single one-way hash
function identifier. The one-way hash function employed by the
TAMP message originator in generating the digital signature MUST
be present.
o encapContentInfo is the signed content, consisting of a content
type identifier and the content itself. The use of the
EncapsulatedContentInfo type is discussed further in
Section 2.2.2.
o certificates is an OPTIONAL collection of certificates. It MAY be
omitted, or it MAY include the X.509 certificates needed to
construct the certification path of the TAMP message originator.
For TAMP messages sent to a trust anchor store where an apex trust
anchor or management trust anchor is used directly to validate the
TAMP message digital signature, this field SHOULD be omitted.
When an apex trust anchor or management trust anchor is used to
validate an X.509 certification path [RFC5280], and the subject
public key from the final certificate in the certification path is
used to validate the TAMP message digital signature, the
certificate of the TAMP message originator SHOULD be included, and
additional certificates to support certification path construction
MAY be included. For TAMP messages sent by a trust anchor store,
this field SHOULD include only the signer's certificate or should
be omitted. A TAMP message recipient MUST NOT reject a valid TAMP
message that contains certificates that are not needed to validate
the digital signature. PKCS#6 extended certificates [PKCS#6] and
attribute certificates (either version 1 or version 2) [RFC5755]
MUST NOT be included in the set of certificates; these certificate
formats are not used in TAMP. Certification authority (CA)
certificates and end entity certificates MUST conform to the
profiles defined in [RFC5280].
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RFC 5934 TAMP August 2010
o crls is an OPTIONAL collection of certificate revocation lists
(CRLs).
o signerInfos is a collection of per-signer information, and for
TAMP, the collection MUST contain exactly one SignerInfo. The use
of the SignerInfo type is discussed further in Section 2.2.1.
2.2.1. SignerInfo
The TAMP message originator is represented in the SignerInfo type.
The fields of SignerInfo are used as follows:
o version is the syntax version number. With TAMP, the version MUST
be set to 3.
o sid identifies the TAMP message originator's public key. The
subjectKeyIdentifier alternative is always used with TAMP, which
identifies the public key directly. When the public key is
included in a TrustAnchorInfo object, this identifier is included
in the keyId field. When the public key is included in a
Certificate or TBSCertificate, this identifier is included in the
subjectKeyIdentifier certificate extension.
o digestAlgorithm identifies the one-way hash function, and any
associated parameters, used by the TAMP message originator. It
MUST contain the one-way hash functions employed by the
originator. This message digest algorithm identifier MUST match
the one carried in the digestAlgorithms field in SignedData. The
message digest algorithm identifier is carried in two places to
facilitate stream processing by the receiver.
o signedAttrs is an OPTIONAL set of attributes that are signed along
with the content. The signedAttrs are OPTIONAL in the CMS, but
signedAttrs is REQUIRED for all signed TAMP messages. The SET OF
Attribute MUST be encoded with the Distinguished Encoding Rules
(DER) [X.690]. Section 2.2.3 of this document lists the signed
attributes that MUST be included in the collection. Other signed
attributes MAY be included, but any unrecognized signed attributes
MUST be ignored.
o signatureAlgorithm identifies the digital signature algorithm, and
any associated parameters, used by the TAMP message originator to
generate the digital signature.
o signature is the digital signature value generated by the TAMP
message originator.
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RFC 5934 TAMP August 2010
o unsignedAttrs is an OPTIONAL set of attributes that are not
signed. For TAMP, this field is usually omitted. It is present
only in Apex Trust Anchor Update messages that are to be validated
using the apex trust anchor contingency public key. In this case,
the SET OF Attribute MUST include the symmetric key needed to
decrypt the contingency public key in the contingency-public-key-
decrypt-key unsigned attribute. Section 2.2.4 of this document
describes this unsigned attribute.
2.2.2. EncapsulatedContentInfo
The EncapsulatedContentInfo structure contains the TAMP message. The
fields of EncapsulatedContentInfo are used as follows:
o eContentType is an object identifier that uniquely specifies the
content type, and for TAMP, the value identifies the TAMP message.
The list of TAMP message content types is provided in Section 4.
o eContent is the TAMP message, encoded as an octet string. In
general, the CMS does not require the eContent to be DER-encoded
before constructing the octet string. However, TAMP messages MUST
be DER-encoded.
2.2.3. Signed Attributes
The TAMP message originator MUST digitally sign a collection of
attributes along with the TAMP message. Each attribute in the
collection MUST be DER-encoded. The syntax for attributes is defined
in [RFC5912].
Each of the attributes used with this CMS profile has a single
attribute value. Even though the syntax is defined as a SET OF
AttributeValue, there MUST be exactly one instance of AttributeValue
present.
The SignedAttributes syntax within SignerInfo is defined as a SET OF
Attribute. The SignedAttributes MUST include only one instance of
any particular attribute. TAMP messages that violate this rule MUST
be rejected as malformed.
The TAMP message originator MUST include the content-type and
message-digest attributes. The TAMP message originator MAY also
include the binary-signing-time attribute.
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RFC 5934 TAMP August 2010
The TAMP message originator MAY include any other attribute that it
deems appropriate. The intent is to allow additional signed
attributes to be included if a future need is identified. This does
not cause an interoperability concern because unrecognized signed
attributes MUST be ignored.
The following summarizes the signed attribute requirements for TAMP
messages:
o content-type MUST be supported.
o message-digest MUST be supported.
o binary-signing-time MAY be supported. When present, it is
generally ignored by the recipient.
o other attributes MAY be supported. Unrecognized attributes MUST
be ignored by the recipient.
2.2.3.1. Content-Type Attribute
The TAMP message originator MUST include a content-type attribute; it
is an object identifier that uniquely specifies the content type.
Section 11.1 of [RFC5652] defines the content-type attribute. For
TAMP, the value identifies the TAMP message. The list of TAMP
message content types and their identifiers is provided in Section 4.
A content-type attribute MUST contain the same object identifier as
the content type contained in the EncapsulatedContentInfo.
2.2.3.2. Message-Digest Attribute
The TAMP message originator MUST include a message-digest attribute,
having as its value the output of a one-way hash function computed on
the TAMP message that is being signed. Section 11.2 of [RFC5652]
defines the message-digest attribute.
2.2.3.3. Binary-Signing-Time Attribute
The TAMP message originator MAY include a binary-signing-time
attribute, specifying the time at which the digital signature was
applied to the TAMP message. The binary-signing-time attribute is
defined in [RFC4049].
No processing of the binary-signing-time attribute is REQUIRED of a
TAMP message recipient; however, the binary-signing-time attribute
MAY be included by the TAMP message originator as a form of message
identifier.
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RFC 5934 TAMP August 20102.2.4. Unsigned Attributes
For TAMP, unsigned attributes are usually omitted. An unsigned
attribute is present only in Apex Trust Anchor Update messages that
are to be validated by the apex trust anchor contingency public key.
In this case, the symmetric key to decrypt the previous contingency
public key is provided in the contingency-public-key-decrypt-key
unsigned attribute. This attribute MUST be supported, and it is
described in Section 2.2.4.1.
The TAMP message originator SHOULD NOT include other unsigned
attributes, and any unrecognized unsigned attributes MUST be ignored.
The UnsignedAttributes syntax within SignerInfo is defined as a SET
OF Attribute. The UnsignedAttributes MUST include only one instance
of any particular attribute. TAMP messages that violate this rule
MUST be rejected as malformed.
2.2.4.1. Contingency-Public-Key-Decrypt-Key Attribute
The contingency-public-key-decrypt-key attribute provides the
plaintext symmetric key needed to decrypt the previously distributed
apex trust anchor contingency public key. The symmetric key MUST be
useable with the symmetric algorithm used to previously encrypt the
contingency public key.
The contingency-public-key-decrypt-key attribute has the following
syntax:
contingency-public-key-decrypt-key ATTRIBUTE ::= {
WITH SYNTAX PlaintextSymmetricKey
SINGLE VALUE TRUE
ID id-aa-TAMP-contingencyPublicKeyDecryptKey }
id-aa-TAMP-contingencyPublicKeyDecryptKey
OBJECT IDENTIFIER ::= { id-attributes 63 }
PlaintextSymmetricKey ::= OCTET STRING
3. Trust Anchor Formats
TAMP recognizes three formats for representing trust anchor
information within the protocol itself: Certificate [RFC5280],
TBSCertificate [RFC5280], and TrustAnchorInfo [RFC5914]. The
TrustAnchorChoice structure, defined in [RFC5914], is used to select
one of these options.
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RFC 5934 TAMP August 2010
TrustAnchorChoice ::= CHOICE {
certificate Certificate,
tbsCert [1] EXPLICIT TBSCertificate,
taInfo [2] EXPLICIT TrustAnchorInfo }
The Certificate structure is commonly used to represent trust
anchors. Certificates include a signature, which removes the ability
for relying parties to customize the information within the structure
itself. TBSCertificate contains all of the information of the
Certificate structure except for the signature, enabling tailoring of
the information. TrustAnchorInfo is intended to serve as a
minimalist representation of trust anchor information for scenarios
where storage or bandwidth is highly constrained.
Implementations are not required to support all three options. The
unsupportedTrustAnchorFormat error code should be indicated when
generating a TAMPError due to receipt of an unsupported trust anchor
format.
4. Trust Anchor Management Protocol Messages
TAMP makes use of signed and unsigned messages. The CMS is used in
both cases. An object identifier is assigned to each TAMP message
type, and this object identifier is used as a content type in the
CMS.
TAMP specifies eleven message types. The following provides the
content type identifier for each TAMP message type, and it indicates
whether a digital signature is required. If the following indicates
that the TAMP message MUST be signed, then implementations MUST
reject a message of that type that is not signed.
o The TAMP Status Query message MUST be signed. It uses the
following object identifier: { id-tamp 1 }.
o The TAMP Status Response message SHOULD be signed. It uses the
following object identifier: { id-tamp 2 }.
o The Trust Anchor Update message MUST be signed. It uses the
following object identifier: { id-tamp 3 }.
o The Trust Anchor Update Confirm message SHOULD be signed. It uses
the following object identifier: { id-tamp 4 }.
o The Apex Trust Anchor Update message MUST be signed. It uses the
following object identifier: { id-tamp 5 }.
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RFC 5934 TAMP August 2010
o The Apex Trust Anchor Update Confirm message SHOULD be signed. It
uses the following object identifier: { id-tamp 6 }.
o The Community Update message MUST be signed. It uses the
following object identifier: { id-tamp 7 }.
o The Community Update Confirm message SHOULD be signed. It uses
the following object identifier: { id-tamp 8 }.
o The Sequence Number Adjust MUST be signed. It uses the following
object identifier: { id-tamp 10 }.
o The Sequence Number Adjust Confirm message SHOULD be signed. It
uses the following object identifier: { id-tamp 11 }.
o The TAMP Error message SHOULD be signed. It uses the following
object identifier: { id-tamp 9 }.
Trust anchor managers generate TAMP Status Query, Trust Anchor
Update, Apex Trust Anchor Update, Community Update, and Sequence
Number Adjust messages. Trust anchor stores generate TAMP Status
Response, Trust Anchor Update Confirm, Apex Trust Anchor Update
Confirm, Community Update Confirm, Sequence Number Adjust Confirm,
and TAMP Error messages.
Support for Trust Anchor Update messages is REQUIRED. Support for
all other message formats is RECOMMENDED. Implementations that
support the HTTP binding described in Appendix C MUST additionally
support Trust Anchor Update Confirm and TAMP Error messages and MAY
support 0 or more of the following pairs of messages: TAMP Status
Query and TAMP Status Query Response; Apex Trust Anchor Update and
Apex Trust Anchor Update Confirm; Community Update and Community
Update Confirm; Sequence Number Adjust and Sequence Number Adjust
Confirm. Implementations that operate in a disconnected manner MUST
NOT assume a response will be received from each consumer of a TAMP
message.
A typical interaction between a trust anchor manager and a trust
anchor store will follow the message flow shown in Figure 1. Figure
1 does not illustrate a flow where an error occurs.
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RFC 5934 TAMP August 2010
+---------+ +----------+
| | Trust Anchor Status Query | |
| |------------------------------->| |
| | | |
| | Trust Anchor Status Response | |
| Trust |<-------------------------------| Trust |
| Anchor | | Anchor |
| Manager | Trust Anchor Update | Store |
| |------------------------------->| |
| | | |
| | Trust Anchor Update Confirm | |
| |<-------------------------------| |
| | | |
+---------+ +----------+
Figure 1. Typical TAMP Message Flow
Each TAMP query and update message includes an indication of the type
of response that is desired. The response can either be terse or
verbose. All trust anchor stores MUST support both the terse and
verbose responses and SHOULD generate a response of the type
indicated in the corresponding request. TAMP response processors
MUST support processing of both terse and verbose responses.
Trust anchor stores SHOULD be able to process and properly act upon
the valid payload of the TAMP Status Query message, the Trust Anchor
Update message, the Apex Trust Anchor Update message, and the
Sequence Number Adjust message. TAMP implementations MAY also
process and act upon the valid payload of the Community Update
message.
TAMP implementations SHOULD support generation of the TAMP Status
Response message, the Trust Anchor Update Confirm message, the Apex
Trust Anchor Update Confirm message, the Sequence Number Adjust
Confirm message, and the TAMP Error message. If a TAMP
implementation supports the Community Update message, then generation
of Community Update Confirm messages SHOULD also be supported.
4.1. TAMP Status Query
The TAMP Status Query message is used to request information about
the trust anchors that are currently installed in a trust anchor
store, and for the list of communities to which the store belongs.
The TAMP Status Query message MUST be signed. For the query message
to be valid, the trust anchor store MUST be an intended recipient of
the query; the sequence number checking described in Section 6 MUST
be successful when the TAMP message signer is a trust anchor; and the
digital signature MUST be validated by the apex trust anchor
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RFC 5934 TAMP August 2010
HardwareSerialEntry ::= CHOICE {
all NULL,
single OCTET STRING,
block SEQUENCE {
low OCTET STRING,
high OCTET STRING } }
CommunityIdentifierList ::= SEQUENCE SIZE (0..MAX) OF Community
Community ::= OBJECT IDENTIFIER
The fields of TAMPStatusQuery are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o terse indicates the type of response that is desired. A terse
response is indicated by a value of 1, and a verbose response is
indicated by a value of 2, which is omitted during encoding since
it is the default value.
o query contains two items: the target and the seqNum. target
identifies the target(s) of the query message. seqNum is a
single-use value that will be used to match the TAMP Status Query
message with the TAMP Status Response message. The sequence
number is also used to detect TAMP message replay. The sequence
number processing described in Section 6 MUST successfully
complete before a response is returned.
The fields of TAMPMsgRef are used as follows:
o target identifies the target(s) of the query. Several
alternatives for naming a target are provided. To identify a
cryptographic module, a combination of a cryptographic type and
serial number are used. The cryptographic type is represented as
an ASN.1 object identifier, and the unique serial number is
represented as a string of octets. To facilitate compact
representation of serial numbers, a contiguous block can be
specified by the lowest included serial number and the highest
included serial number. When present, the high and low octet
strings MUST have the same length. The
HardwareModuleIdentifierList sequence MUST NOT contain duplicate
hwType values, so that each member of the sequence names all of
the cryptographic modules of this type. Object identifiers are
also used to identify communities of trust anchor stores. A
sequence of these object identifiers is used if more than one
community is the target of the message. A trust anchor store is
considered a target if it is a member of any of the listed
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RFC 5934 TAMP August 2010
communities. An explicit NULL value is used to identify all
modules that consider the signer of the TAMP message to be an
authorized source for that message type. The uri field can be
used to identify a target, i.e., a trust anchor store, using a
Uniform Resource Identifier [RFC3986]. Additional name types are
supported via the otherName field, which is of type AnotherName.
AnotherName is defined in [RFC5280]. The format and semantics of
the name are indicated through the OBJECT IDENTIFIER in the type-
id field. The name itself is conveyed as a value field in
otherName. Implementations MUST support the allModules option and
SHOULD support all TargetIdentifier options.
o seqNum contains a single-use value that will be used to match the
TAMP Status Query message with the successful TAMP Status Response
message. The sequence number processing described in Section 6
MUST successfully complete before a response is returned.
To determine whether a particular cryptographic module serial number
is considered part of a specified block, all of the following
conditions MUST be met. First, the cryptographic module serial
number MUST be the same length as both the high and low octet
strings. Second, the cryptographic module serial number MUST be
greater than or equal to the low octet string. Third, the
cryptographic module serial number MUST be less than or equal to the
high octet string.
One octet string is equal to another if they are of the same length
and are the same at each octet position. An octet string, S1, is
greater than another, S2, where S1 and S2 have the same length, if
and only if S1 and S2 have different octets in one or more positions,
and in the first such position, the octet in S1 is greater than that
in S2, considering the octets as unsigned binary numbers. Note that
these octet string comparison definitions are consistent with those
in clause 6 of [X.690].
4.2. TAMP Status Query Response
The TAMP Status Response message is a reply by a trust anchor store
to a valid TAMP Status Query message. The TAMP Status Response
message provides information about the trust anchors that are
currently installed in the trust anchor store and the list of
communities to which the trust anchor store belongs, if any. The
TAMP Status Response message MAY be signed or unsigned. A TAMP
Status Response message MUST be signed if the implementation is
capable of signing it.
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RFC 5934 TAMP August 2010
o response contains either a terse response or a verbose response.
The terse response is represented by TerseStatusResponse, and the
verbose response is represented by VerboseStatusResponse.
o usesApex is a Boolean value that indicates whether the first item
in the TerseStatusResponse.taKeyIds or
VerboseStatusResponse.taInfo field identifies the apex TA.
The fields of TerseStatusResponse are used as follows:
o taKeyIds contains a sequence of key identifiers. Each trust
anchor contained in the trust anchor store is represented by one
key identifier. When TAMPStatusResponse.usesApex is TRUE, the
apex trust anchor is represented by the first key identifier in
the sequence, which contains the key identifier of the operational
public key.
o communities is OPTIONAL. When present, it contains a sequence of
object identifiers. Each object identifier names one community to
which this trust anchor store belongs. When the trust anchor
store belongs to no communities, this field is omitted.
The fields of VerboseStatusResponse are used as follows:
o taInfo contains a sequence of TrustAnchorChoice structures. One
entry in the sequence is provided for each trust anchor contained
in the trust anchor store. When TAMPStatusResponse.usesApex is
TRUE, the apex trust anchor is the first trust anchor in the
sequence.
o continPubKeyDecryptAlg is OPTIONAL. When present, it indicates
the decryption algorithm needed to decrypt the currently installed
apex trust anchor contingency public key, if a contingency key is
associated with the apex trust anchor. When present,
TAMPStatusResponse.usesApex MUST be TRUE.
o communities is OPTIONAL. When present, it contains a sequence of
object identifiers. Each object identifier names one community to
which this trust anchor store belongs. When the trust anchor
store belongs to no communities, this field is omitted.
o tampSeqNumbers is OPTIONAL. When present, it is used to indicate
the currently held sequence number for each trust anchor
authorized to sign TAMP messages. The keyId field identifies the
trust anchor, and the seqNumber field provides the current
sequence number associated with the trust anchor.
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RFC 5934 TAMP August 20104.3. Trust Anchor Update
The Trust Anchor Update message is used to add, remove, and change
management and identity trust anchors. The Trust Anchor Update
message cannot be used to update the apex trust anchor. The Trust
Anchor Update message MUST be signed. For a Trust Anchor Update
message to be valid, the trust anchor store MUST be an intended
recipient of the update; the sequence number checking described in
Section 6 MUST be successful when the TAMP message signer is a trust
anchor; and the digital signature MUST be validated using the apex
trust anchor operational public key, an authorized management trust
anchor, or via an authorized X.509 certification path originating
with such a trust anchor.
If the digital signature on the Trust Anchor Update message is valid,
sequence number checking is successful, the signer is authorized, and
the trust anchor store is an intended recipient of the TAMP message,
then the trust anchor store MUST perform the specified updates and
return a Trust Anchor Update Confirm message. If a Trust Anchor
Update Confirm message is not returned, then a TAMP Error message
SHOULD be returned.
The Trust Anchor Update content type has the following syntax:
tamp-update CONTENT-TYPE ::=
{ TAMPUpdate IDENTIFIED BY id-ct-TAMP-update }
id-ct-TAMP-update OBJECT IDENTIFIER ::= { id-tamp 3 }
TAMPUpdate ::= SEQUENCE {
version [0] TAMPVersion DEFAULT v2,
terse [1] TerseOrVerbose DEFAULT verbose,
msgRef TAMPMsgRef,
updates SEQUENCE SIZE (1..MAX) OF TrustAnchorUpdate,
tampSeqNumbers [2]TAMPSequenceNumbers OPTIONAL }
TrustAnchorUpdate ::= CHOICE {
add [1] TrustAnchorChoice,
remove [2] SubjectPublicKeyInfo,
change [3] EXPLICIT TrustAnchorChangeInfoChoice }
TrustAnchorChangeInfoChoice ::= CHOICE {
tbsCertChange [0] TBSCertificateChangeInfo,
taChange [1] TrustAnchorChangeInfo }
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RFC 5934 TAMP August 2010
TBSCertificateChangeInfo ::= SEQUENCE {
serialNumber CertificateSerialNumber OPTIONAL,
signature [0] AlgorithmIdentifier OPTIONAL,
issuer [1] Name OPTIONAL,
validity [2] Validity OPTIONAL,
subject [3] Name OPTIONAL,
subjectPublicKeyInfo [4] SubjectPublicKeyInfo,
exts [5] EXPLICIT Extensions OPTIONAL }
TrustAnchorChangeInfo ::= SEQUENCE {
pubKey SubjectPublicKeyInfo,
keyId KeyIdentifier OPTIONAL,
taTitle TrustAnchorTitle OPTIONAL,
certPath CertPathControls OPTIONAL,
exts [1] Extensions OPTIONAL }
The fields of TAMPUpdate are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o terse indicates the type of response that is desired. A terse
response is indicated by a value of 1, and a verbose response is
indicated by a value of 2, which is omitted during encoding since
it is the default value.
o msgRef contains two items: the target and the seqNum. target
identifies the target(s) of the update message. The
TargetIdentifier syntax is described in Section 4.1. seqNum is a
single-use value that will be used to match the Trust Anchor
Update message with the Trust Anchor Update Confirm message. The
sequence number is also used to detect TAMP message replay. The
sequence number processing described in Section 6 MUST
successfully complete before any of the updates are processed.
o updates contains a sequence of updates, which are used to add,
remove, and change management or identity trust anchors. Each
entry in the sequence represents one of these actions, and is
indicated by an instance of TrustAnchorUpdate. The actions are a
batch of updates that MUST be processed in the order that they
appear, but each of the updates is processed independently. Each
of the updates MUST satisfy the subordination checks described in
Section 7. Even if one or more of the updates fail, then the
remaining updates MUST be processed. These updates MUST NOT make
any changes to the apex trust anchor.
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RFC 5934 TAMP August 2010
o tampSeqNumbers MAY be included to provide the initial or new
sequence numbers for trust anchors added or changed by the updates
field. Elements included in the tampSeqNumbers field that do not
correspond to an element in the updates field are ignored.
Elements included in the tampSeqNumbers field that do correspond
to an element in the updates field and contain a sequence number
less than or equal to the most recently stored sequence number for
the trust anchor are ignored. Elements included in the
tampSeqNumbers field that do correspond to an element in the
updates field and contain a sequence number greater than the most
recently stored sequence number for the indicated trust anchor are
processed by setting the stored sequence number for the trust
anchor equal to the new value.
The TrustAnchorUpdate is a choice of three structures, and each
alternative represents one of the three possible actions: add,
remove, and change. A description of the syntax associated with each
of these actions follows:
o add is used to insert a new management or identity trust anchor
into the trust anchor store. The TrustAnchorChoice structure is
used to provide the trusted public key and all of the information
associated with it. However, the action MUST fail with the error
code notAuthorized if the subordination checks described in
Section 7 are not satisfied. See Section 3 for a discussion of
the TrustAnchorChoice structure. The apex trust anchor cannot be
introduced into a trust anchor store using this action; therefore,
the id-pe-wrappedApexContinKey MUST NOT be present in the
extensions field. The constraints of the existing trust anchors
are unchanged by this action. An attempt to add a management or
identity trust anchor that is already in place with the same
values for every field in the TrustAnchorChoice structure MUST be
treated as a successful addition. An attempt to add a management
or identity trust anchor that is already present with the same
pubKey values, but with different values for any of the fields in
the TrustAnchorChoice structure, MUST fail with the error code
improperTAAddition. This means a trust anchor may not be added
twice using different TrustAnchorChoice options. If a different
format is desired, the existing trust anchor must be removed and
the new format added.
o remove is used to delete an existing management or identity trust
anchor from the trust anchor store, including the deletion of the
management trust anchor associated with the TAMP message signer.
However, the action MUST fail with the error code notAuthorized if
the subordination checks described in Section 7 are not satisfied.
The public key contained in SubjectPublicKeyInfo names the
management or identity trust anchor to be deleted. An attempt to
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RFC 5934 TAMP August 2010
delete a trust anchor that is not present MUST be treated as a
successful deletion. The constraints of the deleted trust anchor
are not distributed to other trust anchors in any manner. The
apex trust anchor cannot be removed using this action, which
ensures that this action cannot place the trust anchor store in an
unrecoverable configuration.
o change is used to update the information associated with an
existing management or identity trust anchor in the trust anchor
store. Attempts to change a trust anchor added as a Certificate
MUST fail with the error code improperTAChange. The public key
contained in the SubjectPublicKeyInfo field of
TrustAnchorChangeInfo or in the subjectPublicKeyInfo field of a
TBSCertificateChangeInfo names the to-be-updated trust anchor.
However, the action MUST fail with the error code notAuthorized if
the subordination checks described in Section 7 are not satisfied.
An attempt to change a trust anchor that is not present MUST
result in a failure with the trustAnchorNotFound status code. The
TrustAnchorChangeInfo structure or the TBSCertificateChangeInfo
structure is used to provide the revised configuration of the
management or identity trust anchor. If the update fails for any
reason, then the original trust anchor configuration MUST be
preserved. The apex trust anchor information cannot be changed
using this action. Attempts to change a trust anchor added as a
TBSCertificate using a TrustAnchorChangeInfo MUST fail with an
improperTAChange error. Attempts to change a trust anchor added
as a TrustAnchorInfo using a TBSCertificateChangeInfo MUST fail
with an improperTAChange error.
The fields of TrustAnchorChangeInfo are used as follows:
o pubKey contains the algorithm identifier and the public key of the
management or identity trust anchor. It is used to locate the
to-be-updated trust anchor in the trust anchor store.
o keyId is OPTIONAL, and when present, it contains the public key
identifier of the trust anchor public key, which is contained in
the pubKey field. If this field is not present, then the public
key identifier remains unchanged. If this field is present, the
provided public key identifier replaces the previous one.
o taTitle is OPTIONAL, and when present, it provides a human
readable name for the management or identity trust anchor. When
absent in a change trust anchor update, any title that was
previously associated with the trust anchor is removed.
Similarly, when present in a change trust anchor update, the title
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RFC 5934 TAMP August 2010
in the message is associated with the trust anchor. If a previous
title was associated with the trust anchor, then the title is
replaced. If a title was not previously associated with the trust
anchor, then the title from the update message is added.
o certPath is OPTIONAL, and when present, it provides the controls
needed to construct and validate an X.509 certification path.
When absent in a change trust anchor update, any controls that
were previously associated with the management or identity trust
anchor are removed, which means that delegation is no longer
permitted. Similarly, when present in a change trust anchor
update, the controls in the message are associated with the
management or identity trust anchor. If previous controls,
including the trust anchor distinguished name, were associated
with the trust anchor, then the controls are replaced, which means
that delegation continues to be supported, but that different
certification paths will be valid. If controls were not
previously associated with the management or identity trust
anchor, then the controls from the update message are added, which
enables delegation. The syntax and semantics of CertPathControls
are discussed in [RFC5914].
o exts is OPTIONAL, and when present, it provides the extensions
values that are associated with the trust anchor. When absent in
a change trust anchor update, any extensions that were previously
associated with the trust anchor are removed. Similarly, when
present in a change trust anchor update, the extensions in the
message are associated with the trust anchor. Any extensions
previously associated with the trust anchor are replaced or
removed.
The fields of TBSCertificateChangeInfo are used to alter the fields
within a TBSCertificate structure. TBSCertificate is described in
[RFC5280]. For all fields except exts, if the field is absent in a
change trust anchor update, then any previous value associated with a
trust anchor is unchanged. For the exts field, if the field is
absent in a change trust anchor update, then any previous value
associated with a trust anchor is removed. For all fields, if the
field is present in a change trust anchor update, then any previous
value associated with a trust anchor is replaced with the value from
the update message.
4.3.1. Trust Anchor List
[RFC5914] defines the TrustAnchorList structure to convey a list of
trust anchors. TAMP implementations MAY process TrustAnchorList
objects (with eContentType (or contentType) using the id-ct-
trustAnchorList OID defined in [RFC5914]) as equivalent to TAMPUpdate
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RFC 5934 TAMP August 2010
The fields of TAMPUpdateConfirm are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o update identifies the TAMPUpdate message to which the trust anchor
store is responding. The update structure repeats the TAMPMsgRef
from the Trust Anchor Update message (see Section 4.3). The
sequence number processing described in Section 6 MUST
successfully complete before any of the updates are processed.
o confirm contains either a terse update confirmation or a verbose
update confirmation. The terse update confirmation is represented
by TerseUpdateConfirm, and the verbose response is represented by
VerboseUpdateConfirm.
The TerseUpdateConfirm contains a sequence of status codes, one for
each TrustAnchorUpdate structure in the Trust Anchor Update message.
The status codes MUST appear in the same order as the
TrustAnchorUpdate structures to which they apply, and the number of
elements in the status code list MUST be the same as the number of
elements in the trust anchor update list. Each of the status codes
is discussed in Section 5.
The fields of VerboseUpdateConfirm are used as follows:
o status contains a sequence of status codes, one for each
TrustAnchorUpdate structure in the Trust Anchor Update message.
The status codes appear in the same order as the TrustAnchorUpdate
structures to which they apply, and the number of elements in the
status code list MUST be the same as the number of elements in the
trust anchor update list. Each of the status codes is discussed
in Section 5.
o taInfo contains a sequence of TrustAnchorChoice structures. One
entry in the sequence is provided for each trust anchor contained
in the trust anchor store. These represent the state of the trust
anchors after the updates have been processed. When usesApex is
true, the apex trust anchor is the first trust anchor in the
sequence.
o tampSeqNumbers is used to indicate the currently held sequence
number for each trust anchor authorized to sign TAMP messages.
The keyId field identifies the trust anchor, and the seqNumber
field provides the current sequence number associated with the
trust anchor.
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RFC 5934 TAMP August 2010
o usesApex is a Boolean value that indicates whether the first item
in the taInfo field identifies the apex TA.
4.5. Apex Trust Anchor Update
The Apex Trust Anchor Update message replaces the operational public
key and, optionally, the contingency public key associated with the
apex trust anchor. Each trust anchor store has exactly one apex
trust anchor. No constraints are associated with the apex trust
anchor. The public key identifier of the operational public key is
used to identify the apex trust anchor in subsequent TAMP messages.
The digital signature on the Apex Trust Anchor Update message is
validated with either the current operational public key or the
current contingency public key. For the Apex Trust Anchor Update
message that is validated with the operational public key to be
valid, the trust anchor store MUST be a target of the update, the
sequence number MUST be larger than the most recently stored sequence
number for the operational public key, and the digital signature MUST
be validated directly with the operational public key. That is, no
delegation via a certification path is permitted. For the Apex Trust
Anchor Update message that is validated with the contingency public
key to be valid, the trust anchor store MUST be a target of the
update, the provided decryption key MUST properly decrypt the
contingency public key, and the digital signature MUST be validated
directly with the decrypted contingency public key. Again, no
delegation via a certification path is permitted.
If the Apex Trust Anchor Update message is validated using the
operational public key, then sequence number processing is handled
normally, as described in Section 6. If the Apex Trust Anchor Update
message is validated using the contingency public key, then the
TAMPMsgRef sequence number MUST contain a zero value. A sequence
number for subsequent messages that will be validated with the new
operational public key can optionally be provided. If no value is
provided, then the trust anchor store MUST be prepared to accept any
sequence number in the next TAMP message validated with the newly
installed apex trust anchor operational public key. If the Apex
Trust Anchor Update message is valid and the clearTrustAnchors flag
is set to TRUE, then all of the management and identity trust anchors
stored in the trust anchor store MUST be deleted. That is, the new
apex trust anchor MUST be the only trust anchor remaining in the
trust anchor store. If the Apex Trust Anchor Update message is valid
and the clearCommunities flag is set to TRUE, then all community
identifiers stored in the trust anchor store MUST be deleted.
The SignedData structure includes a SignerInfo.sid value, and it
identifies the apex trust anchor public key that will be used to
validate the digital signature on this TAMP message. The public key
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RFC 5934 TAMP August 2010
identifier for the operational public key is known in advance, and it
is stored as part of the apex trust anchor. The public key
identifier for the contingency public key is not known in advance;
however, the presence of the unsigned attribute containing the
symmetric key needed to decrypt the contingency public key
unambiguously indicates that the TAMP message signer used the
contingency private key to sign the Apex Trust Anchor Update message.
If the digital signature on the Apex Trust Anchor Update message is
valid using either the apex trust anchor operational public key or
the apex trust anchor contingency public key, sequence number
checking is successful, and the trust anchor store is an intended
recipient of the TAMP message, then the trust anchor store MUST
update the apex trust anchor and return an Apex Trust Anchor Update
Confirm message. If an Apex Trust Anchor Update Confirm message is
not returned, then a TAMP Error message SHOULD be returned. Note
that the sequence number MUST be zero if the Apex Trust Anchor Update
message is validated with the apex trust anchor contingency public
key.
The Apex Trust Anchor Update content type has the following syntax:
tamp-apex-update CONTENT-TYPE ::=
{ TAMPApexUpdate IDENTIFIED BY id-ct-TAMP-apexUpdate }
id-ct-TAMP-apexUpdate OBJECT IDENTIFIER ::= { id-tamp 5 }
TAMPApexUpdate ::= SEQUENCE {
version [0] TAMPVersion DEFAULT v2,
terse [1] TerseOrVerbose DEFAULT verbose,
msgRef TAMPMsgRef,
clearTrustAnchors BOOLEAN,
clearCommunities BOOLEAN,
seqNumber SeqNumber OPTIONAL,
apexTA TrustAnchorChoice }
The fields of TAMPApexUpdate are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o terse indicates the type of response that is desired. A terse
response is indicated by a value of 1, and a verbose response is
indicated by a value of 2, which is omitted during encoding since
it is the default value.
o msgRef contains two items: the target and the seqNum. target
identifies the target(s) of the Apex Trust Anchor Update message.
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RFC 5934 TAMP August 2010
The TargetIdentifier syntax as described in Section 4.1 is used.
seqNum is a single-use value that will be used to match the Apex
Trust Anchor Update message with the Apex Trust Anchor Update
Confirm message. The sequence number is also used to detect TAMP
message replay if the message is validated with the apex trust
anchor operational public key. The sequence number processing
described in Section 6 MUST successfully complete before any
action is taken. However, seqNum MUST contain a zero value if the
message is validated with the apex trust anchor contingency
public key.
o clearTrustAnchors is a Boolean. If the value is set to TRUE, then
all of the management and identity trust anchors stored in the
trust anchor store MUST be deleted, leaving the newly installed
apex trust anchor as the only trust anchor in the trust anchor
store. If the value is set to FALSE, the other trust anchors MUST
NOT be changed.
o clearCommunities is a Boolean. If the value is set to TRUE, then
all of the community identifiers stored in the trust anchor store
MUST be deleted, leaving none. If the value is set to FALSE, the
list of community identifiers MUST NOT be changed.
o seqNumber is OPTIONAL, and when present, it provides the initial
sequence number for the apex trust anchor. If seqNumber is
absent, the trust anchor store is prepared to accept any sequence
number value for the apex trust anchor operational public key.
o apexTA provides the information for the replacement apex trust
anchor. The TrustAnchorChoice structure is used to provide the
trusted public key and all of the information associated with it.
The pubKey, keyId, taTitle, certPath, and exts fields apply to the
operational public key of the apex trust anchor. The
ApexTrustAnchorInfo certificate extension MAY appear as an
extension. Section 9 describes the WrappedApexContingencyKey
certificate extension.
4.6. Apex Trust Anchor Update Confirm
The Apex Trust Anchor Update Confirm message is a reply by a trust
anchor store to a valid Apex Trust Anchor Update message. The Apex
Trust Anchor Update Confirm message provides success or failure
information for the apex trust anchor update. The Apex Trust Anchor
Update Confirm message MAY be signed or unsigned. An Apex Trust
Anchor Update Confirm message MUST be signed if the trust anchor
store is capable of signing it.
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RFC 5934 TAMP August 2010
The TerseApexUpdateConfirm contains a single status code, indicating
the success or failure of the apex trust anchor update. If the apex
trust anchor update failed, then the status code provides the reason
for the failure. Each of the status codes is discussed in Section 5.
The fields of VerboseApexUpdateConfirm are used as follows:
o status contains a single status code, indicating the success or
failure of the apex trust anchor update. If the apex trust anchor
update failed, then the status code provides the reason for the
failure. Each of the status codes is discussed in Section 5.
o taInfo contains a sequence of TrustAnchorChoice structures. One
entry in the sequence is provided for each trust anchor contained
in the trust anchor store. These represent the state of the trust
anchors after the apex trust anchor update has been processed.
See [RFC5914] for a description of the TrustAnchorInfo structure.
The apex trust anchor is the first trust anchor in the sequence.
o communities is OPTIONAL. When present, it contains a sequence of
object identifiers. Each object identifier names one community to
which this trust anchor store belongs. When the trust anchor
store belongs to no communities, this field is omitted.
o tampSeqNumbers is used to indicate the currently held sequence
number for each trust anchor authorized to sign TAMP messages.
The keyId field identifies the trust anchor, and the seqNumber
field provides the current sequence number associated with the
trust anchor.
4.7. Community Update
The trust anchor store maintains a list of identifiers for the
communities of which it is a member. The Community Update message
can be used to remove or add community identifiers from this list.
The Community Update message MUST be signed. For the Community
Update message to be valid, the trust anchor store MUST be a target
of the update; the sequence number checking described in Section 6
MUST be successful when the TAMP message signer is a trust anchor;
and the digital signature MUST be validated by the apex trust anchor
operational public key, an authorized management trust anchor, or via
an authorized X.509 certification path originating with such a trust
anchor.
If the trust anchor store supports the Community Update message, the
digital signature on the Community Update message is valid, sequence
number checking is successful, the signer is authorized, and the
trust anchor store is an intended recipient of the TAMP message, then
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RFC 5934 TAMP August 2010
the trust anchor store MUST make the specified updates and return a
Community Update Confirm message. If a Community Update Confirm
message is not returned, then a TAMP Error message SHOULD be
returned.
The Community Update message contains a batch of updates, and all of
the updates MUST be accepted for the trust anchor store to return a
successful Community Update Confirm message. The remove updates, if
present, MUST be processed before the add updates. Where remove is
present with an empty list, all community identifiers MUST be
removed. This approach prevents community identifiers that are
intended to be mutually exclusive from being installed by a
successful addition and a failed removal. Where add is present, at
least one community identifier MUST appear in the list.
The Community Update content type has the following syntax:
tamp-community-update CONTENT-TYPE ::=
{ TAMPCommunityUpdate IDENTIFIED BY id-ct-TAMP-communityUpdate }
id-ct-TAMP-communityUpdate OBJECT IDENTIFIER ::= { id-tamp 7 }
TAMPCommunityUpdate ::= SEQUENCE {
version [0] TAMPVersion DEFAULT v2,
terse [1] TerseOrVerbose DEFAULT verbose,
msgRef TAMPMsgRef,
updates CommunityUpdates }
CommunityUpdates ::= SEQUENCE {
remove [1] CommunityIdentifierList OPTIONAL,
add [2] CommunityIdentifierList OPTIONAL }
-- At least one MUST be present
The fields of TAMPCommunityUpdate are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o terse indicates the type of response that is desired. A terse
response is indicated by a value of 1, and a verbose response is
indicated by a value of 2, which is omitted during encoding since
it is the default value.
o msgRef contains two items: the target and the seqNum. target
identifies the target(s) of the update message. The
TargetIdentifier syntax as described in Section 4.1 is used.
seqNum is a single-use value that will be used to match the
Community Update message with the Community Update Confirm
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RFC 5934 TAMP August 2010
message. The sequence number is also used to detect TAMP message
replay. The sequence number processing described in Section 6
MUST successfully complete before any of the updates are
processed.
o updates contains a sequence of community identifiers to be removed
and a sequence of community identifiers to be added. These are
represented by the CommunityUpdates structure.
The CommunityUpdates is a sequence of two OPTIONAL sequences, but at
least one of these sequences MUST be present. The first sequence
contains community identifiers to be removed, and if there are none,
it is absent. Where remove is present with an empty list, all
community identifiers MUST be removed. The second sequence contains
community identifiers to be added, and if there are none, it is
absent. The remove updates, if present, MUST be processed before the
add updates. An error is generated if any of the requested removals
or additions cannot be accomplished. However, requests to remove
community identifiers that are not present are treated as successful
removals. Likewise, requests to add community identifiers that are
already present are treated as successful additions. If an error is
generated, the trust anchor store community list MUST NOT be changed.
A description of the syntax associated with each of these actions
follows:
o remove is used to remove one, multiple, or all community
identifiers from the trust anchor store.
o add is used to insert one or more new community identifiers into
the trust anchor store.
4.8. Community Update Confirm
The Community Update Confirm message is a reply by a trust anchor
store to a valid Community Update message. The Community Update
Confirm message provides success or failure information for the
requested updates. Success is returned only if the whole batch of
updates is successfully processed. If any of the requested updates
cannot be performed, then a failure is indicated, and the set of
community identifiers stored in the trust anchor store is unchanged.
The Community Update Confirm message MAY be signed or unsigned. A
Community Update Confirm message MUST be signed if the trust anchor
store is capable of signing it.
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The Community Update Confirm content type has the following syntax:
tamp-community-update-confirm CONTENT-TYPE ::=
{ TAMPCommunityUpdateConfirm IDENTIFIED BY
id-ct-TAMP-communityUpdateConfirm }
id-ct-TAMP-communityUpdateConfirm OBJECT IDENTIFIER ::=
{ id-tamp 8 }
TAMPCommunityUpdateConfirm ::= SEQUENCE {
version [0] TAMPVersion DEFAULT v2,
update TAMPMsgRef,
commConfirm CommunityConfirm }
CommunityConfirm ::= CHOICE {
terseCommConfirm [0] TerseCommunityConfirm,
verboseCommConfirm [1] VerboseCommunityConfirm }
TerseCommunityConfirm ::= StatusCode
VerboseCommunityConfirm ::= SEQUENCE {
status StatusCode,
communities CommunityIdentifierList OPTIONAL }
The fields of TAMPCommunityUpdateConfirm are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o update identifies the Community Update message to which the trust
anchor store is responding. The update structure repeats the
TAMPMsgRef from the Community Update message (see Section 4.7).
The sequence number processing described in Section 6 MUST
successfully complete before any of the updates are processed.
o commConfirm contains either a terse community update confirmation
or a verbose community update confirmation. The terse response is
represented by TerseCommunityConfirm, and the verbose response is
represented by VerboseCommunityConfirm.
The TerseCommunityConfirm contains a single status code, indicating
the success or failure of the Community Update message processing.
If the community update failed, then the status code indicates the
reason for the failure. Each of the status codes is discussed in
Section 5.
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RFC 5934 TAMP August 2010
The fields of VerboseCommunityConfirm are used as follows:
o status contains a single status code, indicating the success or
failure of the Community Update message processing. If the
community update failed, then the status code indicates the reason
for the failure. Each of the status codes is discussed in
Section 5.
o communities is OPTIONAL. When present, it contains the sequence
of community identifiers present in the trust anchor store after
the update is processed. When the trust anchor store belongs to
no communities, this field is omitted.
4.9. Sequence Number Adjust
The trust anchor store maintains the current sequence number for the
apex trust anchor and each management trust anchor authorized for
TAMP messages. Sequence number processing is discussed in Section 6.
The Sequence Number Adjust message can be used to provide the most
recently used sequence number to one or more targets, thereby
reducing the possibility of replay. The Sequence Number Adjust
message MUST be signed. For the Sequence Number Adjust message to be
valid, the trust anchor store MUST be an intended recipient of the
Sequence Number Adjust message, the sequence number MUST be equal to
or larger than the most recently stored sequence number for the
originating trust anchor, and the digital signature MUST be validated
by the apex trust anchor operational public key or an authorized
management trust anchor.
If the digital signature on the Sequence Number Adjust message is
valid, the sequence number is equal to or larger than the most
recently stored sequence number for the originating trust anchor, the
signer is authorized, and the trust anchor store is an intended
recipient of the TAMP message, then the trust anchor store MUST
update the sequence number associated with the originating trust
anchor and return a Sequence Number Adjust Confirm message. If a
Sequence Number Adjust Confirm message is not returned, then a TAMP
Error message SHOULD be returned.
The Sequence Number Adjust message contains an adjustment for the
sequence number of the TAMP message signer.
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RFC 5934 TAMP August 2010
The Sequence Number Adjust content type has the following syntax:
tamp-sequence-number-adjust CONTENT-TYPE ::=
{ SequenceNumberAdjust IDENTIFIED BY id-ct-TAMP-seqNumAdjust }
id-ct-TAMP-seqNumAdjust OBJECT IDENTIFIER ::= { id-tamp 10 }
SequenceNumberAdjust ::= SEQUENCE {
Version [0] TAMPVersion DEFAULT v2,
msgRef TAMPMsgRef }
The fields of SequenceNumberAdjust are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o msgRef contains two items: the target and the seqNum. target
identifies the target(s) of the sequence number adjust message.
The TargetIdentifier syntax as described in Section 4.1 is used.
The allModules target is expected to be used for Sequence Number
Adjust messages. seqNum MUST be equal to or larger than the most
recently stored sequence number for this TAMP message signer, and
the value will be used to match the Sequence Number Adjust message
with the Sequence Number Adjust Confirm message. The sequence
number processing described in Section 6 applies, except that the
sequence number in a Sequence Number Adjust message is acceptable
if it matches the most recently stored sequence number for this
TAMP message signer. If sequence number checking completes
successfully, then the sequence number is adjusted; otherwise, it
remains unchanged.
4.10. Sequence Number Adjust Confirm
The Sequence Number Adjust Confirm message is a reply by a trust
anchor store to a valid Sequence Number Adjust message. The Sequence
Number Adjust Confirm message provides success or failure
information. Success is returned only if the sequence number for the
trust anchor that signed the Sequence Number Adjust message
originator is adjusted. If the sequence number cannot be adjusted,
then a failure is indicated, and the sequence number stored in the
trust anchor store is unchanged. The Sequence Number Adjust Confirm
message MAY be signed or unsigned. A Sequence Number Adjust Confirm
message MUST be signed if the trust anchor store is capable of
signing it.
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RFC 5934 TAMP August 2010
The Sequence Number Adjust Confirm content type has the following
syntax:
tamp-sequence-number-adjust-confirm CONTENT-TYPE ::=
{ SequenceNumberAdjustConfirm IDENTIFIED BY
id-ct-TAMP-seqNumAdjustConfirm }
id-ct-TAMP-seqNumAdjustConfirm OBJECT IDENTIFIER ::=
{ id-tamp 11 }
SequenceNumberAdjustConfirm ::= SEQUENCE {
version [0] TAMPVersion DEFAULT v2,
adjust TAMPMsgRef,
status StatusCode }
The fields of SequenceNumberAdjustConfirm are used as follows:
o version identifies version of TAMP. For this version of the
specification, the default value, v2, MUST be used.
o adjust identifies the Sequence Number Adjust message to which the
trust anchor store is responding. The adjust structure repeats
the TAMPMsgRef from the Sequence Number Adjust message (see
Section 4.9). The sequence number processing described in
Section 6 MUST successfully complete to adjust the sequence number
associated with the Sequence Number Adjust message originator.
o status contains a single status code, indicating the success or
failure of the Sequence Number Adjust message processing. If the
adjustment failed, then the status code indicates the reason for
the failure. Each of the status codes is discussed in Section 5.
4.11. TAMP Error
The TAMP Error message is a reply by a trust anchor store to any
invalid TAMP message. The TAMP Error message provides an indication
of the reason for the error. The TAMP Error message MAY be signed or
unsigned. A TAMP Error message MUST be signed if the trust anchor
store is capable of signing it. For the request types defined in
this specification, TAMP Error messages MUST NOT be used to indicate
a request message was successfully processed. Each TAMP Error
message identifies the type of TAMP message that caused the error.
In cases where the TAMP message type cannot be determined, errors MAY
be returned via other means, such as at the protocol level, via an
attached display, etc.
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RFC 5934 TAMP August 2010
notAuthorized (11),
badDigestAlgorithm (12),
badSignatureAlgorithm (13),
unsupportedKeySize (14),
unsupportedParameters (15),
signatureFailure (16),
insufficientMemory (17),
unsupportedTAMPMsgType (18),
apexTAMPAnchor (19),
improperTAAddition (20),
seqNumFailure (21),
contingencyPublicKeyDecrypt (22),
incorrectTarget (23),
communityUpdateFailed (24),
trustAnchorNotFound (25),
unsupportedTAAlgorithm (26),
unsupportedTAKeySize (27),
unsupportedContinPubKeyDecryptAlg (28),
missingSignature (29),
resourcesBusy (30),
versionNumberMismatch (31),
missingPolicySet (32),
revokedCertificate (33),
unsupportedTrustAnchorFormat (34),
improperTAChange (35),
malformed (36),
cmsError (37),
unsupportedTargetIdentifier (38),
other (127) }
The various values of StatusCode are used as follows:
o success is used to indicate that an update, portion of an update,
or adjust was processed successfully.
o decodeFailure is used to indicate that the trust anchor store was
unable to successfully decode the provided message. The specified
content type and the provided content do not match.
o badContentInfo is used to indicate that the ContentInfo syntax is
invalid or that the contentType carried within the ContentInfo is
unknown or unsupported.
o badSignedData is used to indicate that the SignedData syntax is
invalid, the version is unknown or unsupported, or more than one
entry is present in digestAlgorithms.
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RFC 5934 TAMP August 2010
o badEncapContent is used to indicate that the
EncapsulatedContentInfo syntax is invalid. This error can be
generated due to problems located in SignedData.
o badCertificate is used to indicate that the syntax for one or more
certificates in CertificateSet is invalid.
o badSignerInfo is used to indicate that the SignerInfo syntax is
invalid, or the version is unknown or unsupported.
o badSignedAttrs is used to indicate that the signedAttrs syntax
within SignerInfo is invalid.
o badUnsignedAttrs is used to indicate that the unsignedAttrs syntax
within SignerInfo is invalid.
o missingContent is used to indicate that the OPTIONAL eContent is
missing in EncapsulatedContentInfo, which is REQUIRED in this
specification. This error can be generated due to problems
located in SignedData.
o noTrustAnchor is used to indicate one of two possible error
situations. In one case, the subjectKeyIdentifier does not
identify the public key of a trust anchor or a certification path
that terminates with an installed trust anchor. In the other
case, the issuerAndSerialNumber is used to identify the TAMP
message signer, which is prohibited by this specification.
o notAuthorized is used to indicate one of two possible error
situations. In one case, the sid within SignerInfo leads to an
installed trust anchor, but that trust anchor is not an authorized
signer for the received TAMP message content type. Identity trust
anchors are not authorized signers for any of the TAMP message
content types. In the other case, the signer of a Trust Anchor
Update message is not authorized to manage the to-be-updated trust
anchor as determined by a failure of the subordination processing
in Section 7.
o badDigestAlgorithm is used to indicate that the digestAlgorithm in
either SignerInfo or SignedData is unknown or unsupported.
o badSignatureAlgorithm is used to indicate that the
signatureAlgorithm in SignerInfo is unknown or unsupported.
o unsupportedKeySize is used to indicate that the signatureAlgorithm
in SignerInfo is known and supported, but the TAMP message digital
signature could not be validated because an unsupported key size
was employed by the signer.
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RFC 5934 TAMP August 2010
o unsupportedParameters is used to indicate that the
signatureAlgorithm in SignerInfo is known, but the TAMP message
digital signature could not be validated because unsupported
parameters were employed by the signer.
o signatureFailure is used to indicate that the signatureAlgorithm
in SignerInfo is known and supported, but the digital signature in
the signature field within SignerInfo could not be validated.
o insufficientMemory indicates that the update could not be
processed because the trust anchor store did not have sufficient
memory to store the resulting trust anchor configuration or
community identifier.
o unsupportedTAMPMsgType indicates that the TAMP message could not
be processed because the trust anchor store does not support the
provided TAMP message type. This code will be used if the
id-ct-TAMP-communityUpdate content type is provided and the trust
anchor store does not support the Community Update message. This
status code will also be used if the contentType value within
eContentType is not one that is defined in this specification.
o apexTAMPAnchor indicates that the update could not be processed
because the Trust Anchor Update message tried to remove the apex
trust anchor.
o improperTAAddition indicates that a trust anchor update is trying
to add a new trust anchor that may already exist, but some
attributes of the to-be-added trust anchor are being modified in
an improper manner. The desired trust anchor configuration may be
attainable with a change operation instead of an add operation.
o seqNumFailure indicates that the TAMP message could not be
processed because the processing of the sequence number, which is
described in Section 6, resulted in an error.
o contingencyPublicKeyDecrypt indicates that the update could not be
processed because an error occurred while decrypting the
contingency public key.
o incorrectTarget indicates that the query, update, or adjust
message could not be processed because the trust anchor store is
not the intended recipient.
o communityUpdateFailed indicates that the community update
requested the addition of a community identifier or the removal of
a community identifier, but the request could not be honored.
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RFC 5934 TAMP August 2010
o trustAnchorNotFound indicates that a change to a trust anchor was
requested, but the referenced trust anchor is not represented in
the trust anchor store.
o unsupportedTAAlgorithm indicates that an update message would
result in the trust anchor with a public key associated with a
digital signature validation algorithm that is not implemented.
In addition, this status code is used if the algorithm is
supported, but the parameters associated with the algorithm are
not supported.
o unsupportedTAKeySize indicates that the trust anchor would include
a public key of a size that is not supported.
o unsupportedContinPubKeyDecryptAlg indicates that the decryption
algorithm for the apex trust anchor contingency public key is not
supported.
o missingSignature indicates that an unsigned TAMP message was
received, but the received TAMP message type MUST be signed.
o resourcesBusy indicates that the resources necessary to process
the TAMP message are not available at the present time, but the
resources might be available at some point in the future.
o versionNumberMismatch indicates that the version number in a
received TAMP message is not acceptable.
o missingPolicySet indicates that the policyFlags associated with a
trust anchor are set in a fashion that requires the policySet to
be present, but the policySet is missing.
o revokedCertificate indicates that one or more of the certificates
needed to properly process the TAMP message have been revoked.
o unsupportedTrustAnchorFormat indicates that an unsupported trust
anchor format was presented or the version is unknown or
unsupported.
o improperTAChange indicates that a trust anchor update is trying to
change a new trust anchor using a format different than the format
of the existing trust anchor.
o malformed indicates an error in the composition of the CMS
structure encapsulating a TAMP message.
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RFC 5934 TAMP August 2010
o cmsError indicates an error processing a CMS structure that
encapsulated a TAMP message, such as an error processing
ContentType or MessageDigest attributes.
o unsupportedTargetIdentifier indicates that a msgRef with an
unsupported TargetIdentifier option was encountered.
o other indicates that the update could not be processed, but the
reason is not covered by any of the assigned status codes. Use of
this status code SHOULD be avoided.
6. Sequence Number Processing
The sequence number processing facilities in TAMP represent a balance
between replay protection, operational considerations, and trust
anchor store memory management. The goal is to provide replay
protection without making TAMP difficult to use, creating an
environment where surprising error conditions occur on a regular
basis, or imposing onerous memory management requirements on
implementations. This balance is achieved by performing sequence
number checking on TAMP messages that are validated directly using a
trust anchor, and allowing these checks to be skipped whenever the
TAMP message originator is not represented by a trust anchor.
Implementations MUST perform sequence number checking on TAMP
messages that are validated directly using a trust anchor and MAY
perform sequence number checking for TAMP messages validated using a
certification path.
The TAMP Status Query, Trust Anchor Update, Apex Trust Anchor Update,
Community Update, and Sequence Number Adjust messages include a
sequence number. This single-use identifier is used to match a TAMP
message with the response to that TAMP message. When the TAMP
message is validated directly using a trust anchor, the sequence
number is also used to detect TAMP message replay.
To provide replay protection, each TAMP message originator MUST treat
the sequence number as a monotonically increasing non-negative
integer. The sequence number counter is associated with the signing
operation performed by the private key. The trust anchor store MUST
ensure that a newly received TAMP message that is validated directly
by a trust anchor public key contains a sequence number that is
greater than the most recent successfully processed TAMP message from
that originator. Note that the Sequence Number Adjust message is
considered valid if the sequence number is greater than or equal to
the most recent successfully processed TAMP message from that
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RFC 5934 TAMP August 2010
originator. If the sequence number in a received TAMP message does
not meet these conditions, then the trust anchor store MUST reject
the TAMP message, returning a sequence number failure (seqNumFailure)
error.
Whenever a trust anchor is authorized for TAMP messages, either as a
newly installed trust anchor or as a modification to an existing
trust anchor, if a sequence number value is not provided in the Trust
Anchor Update message, memory MUST be allocated for the sequence
number and set to zero. The first TAMP message received that is
validated using that trust anchor is not rejected based on sequence
number checks, and the sequence number from that first TAMP message
is stored. The TAMP message recipient MUST maintain a database of
the most recent sequence number from a successfully processed TAMP
message from a trust anchor. The index for this database is the
trust anchor public key. This could be the apex trust anchor
operational public key or a management trust anchor public key. In
the first case, the apex trust anchor operational public key is used
directly to validate the TAMP message digital signature. In the
second case, a management trust anchor public key is used directly to
validate the TAMP message digital signature.
Sequence number values MUST be 64-bit non-negative integers. Since
ASN.1 encoding of an INTEGER always includes a sign bit, a TAMP
message signer can generate 9,223,372,036,854,775,807 TAMP messages
before exhausting the 64-bit sequence number space, before which the
TAMP message signer MUST transition to a different public/private key
pair. The ability to reset a sequence number provided by the Trust
Anchor Update and Sequence Number Adjust messages is not intended to
avoid the transition to a different key pair; rather, it is intended
to aid recovery from operational errors. A relatively small non-
volatile storage requirement is imposed on the trust anchor store for
the apex trust anchor and each management trust anchor authorized for
TAMP messages.
When the apex trust anchor or a management trust anchor is replaced
or removed from the trust anchor store, the associated sequence
number storage SHOULD be reclaimed.
7. Subordination Processing
When a TAMP update message is processed, several checks are
performed:
o TAMP message authentication is checked including, if necessary,
building and validating a certification path to the signer.
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RFC 5934 TAMP August 2010
o The signer's authorization is checked, including authorization to
manage trust anchors included in the update message.
o Calculation of the trust anchor information to be stored.
This section describes how to perform the second and third steps.
Section 1.2 discusses authentication of TAMP messages. Where a trust
anchor is represented as a certificate and the calculation of the
trust anchor information to be stored is different than the
information in the certificate, the TAMP update fails. The TAMP
message signer may then wrap the certificate inside a TrustAnchorInfo
structure to assert the intended information.
The apex trust anchor is unconstrained, which means that
subordination checking need not be performed on Trust Anchor Update
messages signed with the apex trust anchor operational public key and
that trust anchor information can be stored as it appears in the
update message. Subordination checking is performed as part of the
validation process of all other Trust Anchor Update messages.
For a Trust Anchor Update message that is not signed with the apex
trust anchor operational public key to be valid, the digital
signature MUST be validated using an authorized trust anchor, either
directly or via an X.509 certification path originating with the apex
trust anchor operational public key or an authorized management trust
anchor. The following subordination checks MUST also be performed as
part of validation of the update message.
Each Trust Anchor Update message contains one or more individual
updates, each of which is used to add, modify, or remove a trust
anchor. For each individual update, the constraints of the TAMP
message signer MUST be greater than or equal to the constraints of
the trust anchor in the update. Specifically, constraints included
in the CertPathControls field of a TrustAnchorInfo object (or
equivalent extensions in Certificate or TBSCertificate objects) must
be checked as described below. [RFC5280] describes how the
intersection and union operations referenced below are performed.
o The values of the policy flags stored with a trust anchor as the
result of a TAMPUpdate are either true or equal to the value of
the policy flags associated with the TAMP message signer, i.e., an
update may set a flag to false only if the value associated with
the TAMP message signer is false. The policy flags associated
with the TAMP message signer are read from the policyFlags field
or policyConstraints and inhibitAnyPolicy extensions if the signer
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RFC 5934 TAMP August 2010
is represented as a trust anchor or from the explicit_policy,
policy_mapping, and inhibit_anyPolicy state variables following
path validation if the signer is not represented as a trust
anchor.
o The certificate policies stored with a trust anchor as the result
of a TAMPUpdate are equal to the intersection of the value of the
certificate policies associated with the TAMP message signer and
the value of the policySet field or certificatePolicies extension
from the update. The certificate policies associated with the
TAMP message signer are read from the policySet field in a
TrustAnchorInfo or certificatePolicies extension in a Certificate
or TBSCertificate if the signer is represented as a trust anchor
or from the valid_policy_tree returned following path validation
if the signer is not represented by a trust anchor. Where the
TAMP message signer is represented as a trust anchor, no policy
mapping is performed. If the intersection is NULL and the
to-be-stored requireExplicitPolicy value is true, the TAMP update
fails.
o The excluded names stored with a trust anchor as the result of a
TAMPUpdate are equal to the union of the excluded names associated
with the TAMP message signer and the value from the nameConstr
field or nameConstraints extension from the update. The name
constraints associated with the TAMP message signer are read from
the nameConstr field in a TrustAnchorInfo or nameConstraints
extension in a Certificate or TBSCertificate if the signer is a
trust anchor or from the excludedSubtrees state variable following
path validation if the signer is not a trust anchor. The name of
the trust anchor included in the update MUST NOT fall within the
excluded name space of the TAMP signer. If the name of the trust
anchor falls within the excluded name space of the TAMP signer,
the TAMP update fails.
o The permitted names stored with a trust anchor as the result of a
TAMPUpdate are equal to the intersection of the permitted names
associated with the TAMP message signer and the value from the
nameConstr field or nameConstraints extension from the update.
The name constraints associated with the TAMP message signer are
read from the nameConstr field in a TrustAnchorInfo or
nameConstraints extension in a Certificate or TBSCertificate if
the signer is a trust anchor or from the permittedSubtrees state
variable following path validation if the signer is not a trust
anchor. The name of the trust anchor included in the update MUST
fall within the permitted name space of the TAMP signer. If the
name of the trust anchor does not fall within the permitted name
space of the TAMP signer, the TAMP update fails. If the
intersection is NULL for all name forms, the TAMP update fails.
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RFC 5934 TAMP August 2010
No other extensions defined in [RFC5280] must be processed as part of
subordination processing. Other extensions may define subordination
rules.
8. Implementation Considerations
A public key identifier is used to identify a TAMP message signer.
Since there is no guarantee that the same public key identifier is
not associated with more than one public key, implementations MUST be
prepared for one or more trust anchors to have the same public key
identifier. In practical terms, this means that when a digital
signature validation fails, the implementation MUST see if there is
another trust anchor with the same public key identifier that can be
used to validate the digital signature. While duplicate public key
identifiers are expected to be rare, implementations MUST NOT fail to
find the correct trust anchor when they do occur.
An X.500 distinguished name is used to identify certificate issuers
and certificate subjects. The same X.500 distinguished name can be
associated with more than one trust anchor. However, the trust
anchor public key will be different. The probability that two trust
anchors will have the same X.500 distinguished name and the same
public key identifier but a different public key is diminishingly
small. Therefore, the authority key identifier certificate extension
can be used to resolve X.500 distinguished name collisions.
TAMP assumes a reliable underlying transport protocol.
9. Wrapped Apex Contingency Key Certificate Extension
An apex trust anchor MAY contain contingency key information using
the WrappedApexContingencyKey extension. The extension uses the
ApexContingencyKey structure as defined below.
ApexContingencyKey ::= SEQUENCE {
wrapAlgorithm AlgorithmIdentifier OPTIONAL,
wrappedContinPubKey OCTET STRING OPTIONAL }
The fields of ApexContingencyKey are used as described below. When
one field is present, both MUST be present. When one field is
absent, both MUST be absent. The fields are allowed to be absent to
enable usage of this extension as a means of indicating that the
corresponding public key is recognized as an apex trust anchor by
some relying parties.
o wrapAlgorithm identifies the symmetric algorithm used to encrypt
the apex trust anchor contingency public key. If this public key
is ever needed, the symmetric key needed to decrypt it will be
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RFC 5934 TAMP August 2010
provided in the message that is to be validated using it. The
algorithm identifier is an AlgorithmIdentifier, which contains an
object identifier and OPTIONAL parameters. The object identifier
indicates the syntax of the parameters, if present.
o wrappedContinPubKey is the encrypted apex trust anchor contingency
public key. Once decrypted, it yields the PublicKeyInfo
structure, which consists of the algorithm identifier followed by
the public key itself. The algorithm identifier is an
AlgorithmIdentifier that contains an object identifier and
OPTIONAL parameters. The object identifier indicates the format
of the public key and the syntax of the parameters, if present.
The public key is encoded as a BIT STRING.
The WrappedApexContingencyKey certificate extension MAY be critical,
and it MUST appear at most one time in a set of extensions. The apex
trust anchor info extension is identified by the
id-pe-wrappedApexContinKey object identifier:
id-pe-wrappedApexContinKey OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) pe(1) 20 }
10. Security Considerations
The majority of this specification is devoted to the syntax and
semantics of TAMP messages. It relies on other specifications,
especially [RFC5914], [RFC3852], and [RFC5280], for the syntax and
semantics of trust anchors, intermediate CMS content types, and X.509
certificates, respectively. Since TAMP messages that change the
trust anchor state of a trust anchor store are always signed by a
Trust Anchor Manager, no further data integrity or data origin
authentication mechanisms are needed; however, no confidentiality for
these messages is provided. Similarly, certificates are digitally
signed, and no additional data integrity or data origin
authentication mechanisms are needed. Trust anchor configurations,
Trust Anchor Manager certificates, and trust anchor store
certificates are not intended to be sensitive. As a result, this
specification does not provide for confidentiality of TAMP messages.
Security factors outside the scope of this specification greatly
affect the assurance provided. The procedures used by certification
authorities (CAs) to validate the binding of the subject identity to
their public key greatly affect the assurance associated with the
resulting certificate. This is particularly important when issuing
certificates to other CAs. In the context of TAMP, the issuance of
an end entity certificate under a management trust anchor is an act
of delegation. However, such end entities cannot further delegate.
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RFC 5934 TAMP August 2010
On the other hand, issuance of a CA certificate under a management
trust anchor is an act of delegation where the CA can perform further
delegation. The scope of the delegation can be constrained by
including appropriate certificate extensions in a CA certificate.
X.509 certification path construction involves comparison of X.500
distinguished names. Inconsistent application of name comparison
rules can result in acceptance of invalid X.509 certification paths
or rejection of valid ones. Name comparison can be extremely
complex. To avoid imposing this complexity on trust anchor stores,
any certificate profile used with TAMP SHOULD employ simple name
structures and impose rigorous restrictions on acceptable
distinguished names, including the way that they are encoded. The
goal of that certificate profile should be to enable simple binary
comparison. That is, case conversion, character set conversion,
white space compression, and leading and trailing white space
trimming SHOULD be avoided.
Some digital signature algorithms (DSAs) require the generation of
random one-time values. For example, when generating a DSA digital
signature, the signer MUST generate a random k value [DSS]. Also,
the generation of public/private key pairs relies on random numbers.
The use of an inadequate random number generator (RNG) or an
inadequate pseudo-random number generator (PRNG) to generate such
cryptographic values can result in little or no security. An
attacker may find it much easier to reproduce the random number
generation environment, searching the resulting small set of
possibilities, rather than brute-force searching the whole space.
Compromise of an identity trust anchor private key permits
unauthorized parties to issue certificates that will be acceptable to
all trust anchor stores configured with the corresponding identity
trust anchor. The unauthorized private key holder will be limited by
the certification path controls associated with the identity trust
anchor. For example, clearance constraints in the identity trust
anchor will determine the clearances that will be accepted in
certificates that are issued by the unauthorized private key holder.
Compromise of a management trust anchor private key permits
unauthorized parties to generate signed messages that will be
acceptable to all trust anchor stores configured with the
corresponding management trust anchor. All devices that include the
compromised management trust anchor can be configured as desired by
the unauthorized private key holder within the limits of the
subordination checks described in Section 7. If the management trust
anchor is associated with content types other than TAMP, then the
unauthorized private key holder can generate signed messages of that
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RFC 5934 TAMP August 2010
type. For example, if the management trust anchor is associated with
firmware packages, then the unauthorized private key holder can
install different firmware.
Compromise of the apex trust anchor operational private key permits
unauthorized parties to generate signed messages that will be
acceptable to all trust anchor stores configured with the
corresponding apex trust anchor. All devices that include that apex
trust anchor can be configured as desired by the unauthorized private
key holder, and the unauthorized private key holder can generate
signed messages of any content type. The optional contingency
private key offers a potential way to recover from such a compromise.
The compromise of a CA's private key leads to the same type of
problems as the compromise of an identity or a management trust
anchor private key. The unauthorized private key holder will be
limited by the certification path controls and extensions associated
with the trust anchor.
The compromise of an end entity private key leads to the same type of
problems as the compromise of an identity or a management trust
anchor private key, except that the end entity is unable to issue any
certificates. The unauthorized private key holder will be limited by
the certification path controls and extensions associated with the
trust anchor.
Compromise of a trust anchor store's digital signature private key
permits unauthorized parties to generate signed TAMP response
messages, masquerading as the trust anchor store.
Premature disclosure of the key-encryption key used to encrypt the
apex trust anchor contingency public key may result in early exposure
of the apex trust anchor contingency public key.
TAMP implementations need to be able to parse messages and
certificates. Care must be taken to ensure that there are no
implementation defects in the TAMP message parser or the processing
that acts on the message content. A validation suite is one way to
increase confidence in the parsing of TAMP messages, CMS content
types, attributes, certificates, and extensions.
TrustAnchorList messages do not provide a replay detection mechanism.
Where TrustAnchorList messages are accepted as an alternative means
of adding trust anchors to a trust anchor store, applications may
require additional mechanisms to address the risks associated with
replay of old TrustAnchorList messages.
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RFC 5934 TAMP August 2010
As sequence number values are used to detect replay attempts, trust
anchor store managers must take care to maintain their own sequence
number state, i.e., knowledge of which sequence number to include in
the next TAMP message generated by the trust anchor store manager.
Loss of sequence number state can result in generation of TAMP
messages that cannot be processed due to seqNumFailure. In the event
of loss, sequence number state can be restored by inspecting the most
recently generated TAMP message, provided the messages are logged, or
in collaboration with a trust anchor store manager who can
successfully issue a TAMPStatusQuery message.
11. IANA Considerations
The details of TAMP requests and responses are communicated using
object identifiers (OIDs). The objects are defined in an arc
delegated by IANA to the PKIX working group. This document also
includes eleven media type registrations in Appendix B. No further
action by IANA is necessary for this document or any anticipated
updates.
12. References12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee,
"Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616,
June 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 5652, September 2009.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC5912, June 2010.
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RFC 5934 TAMP August 2010
Additional information:
Magic number(s): None
File extension(s): .ter
Macintosh File Type Code(s):
Person & email address to contact for further information:
Sam Ashmore - srashmo@radium.ncsc.mil
Intended usage: LIMITED USE
Restrictions on usage: None
Author: Sam Ashmore - srashmo@radium.ncsc.mil
Change controller: IESG
Appendix C. TAMP over HTTP
This appendix describes the formatting and transportation conventions
for the TAMP messages when carried by HTTP [RFC2616]. Each TAMP
message type is covered by a subsection below. Each TAMP request
message sent via HTTP is responded to either with an HTTP response
containing a TAMP response or error or, if failure occurs prior to
invoking TAMP, an HTTP error. TAMP response, confirmation, and error
messages are not suitable for caching. In order for TAMP clients and
servers using HTTP to interoperate, the following rules apply.
o Clients MUST use the POST method to submit their requests.
o Servers MUST use the 200 response code for successful responses.
o Clients MAY attempt to send HTTPS requests using Transport Layer
Security (TLS) 1.0 or later, although servers are not required to
support TLS.
o Servers MUST NOT assume client support for any type of HTTP
authentication such as cookies, Basic authentication, or Digest
authentication.
o Clients and servers are expected to follow the other rules and
restrictions in [RFC2616]. Note that some of those rules are for
HTTP methods other than POST; clearly, only the rules that apply
to POST are relevant for this specification.
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RFC 5934 TAMP August 2010C.1. TAMP Status Query Message
A TAMP Status Query Message using the POST method is constructed as
follows: The Content-Type header MUST have the value "application/
tamp-status-query".
The body of the message is the binary value of the DER encoding of
the TAMPStatusQuery, wrapped in a CMS body as described in Section 2.
C.2. TAMP Status Response Message
An HTTP-based TAMP Status Response message is composed of the
appropriate HTTP headers, followed by the binary value of the DER
encoding of the TAMPStatusResponse, wrapped in a CMS body as
described in Section 2.
The Content-Type header MUST have the value "application/
tamp-status-response."
C.3. Trust Anchor Update Message
A Trust Anchor Update Message using the POST method is constructed as
follows: The Content-Type header MUST have the value "application/
tamp-update".
The body of the message is the binary value of the DER encoding of
the TAMPUpdate, wrapped in a CMS body as described in Section 2.
C.4. Trust Anchor Update Confirm Message
An HTTP-based Trust Anchor Update Confirm message is composed of the
appropriate HTTP headers, followed by the binary value of the DER
encoding of the TAMPUpdateConfirm, wrapped in a CMS body as described
in Section 2.
The Content-Type header MUST have the value "application/
tamp-update-confirm".
C.5. Apex Trust Anchor Update Message
An Apex Trust Anchor Update Message using the POST method is
constructed as follows: The Content-Type header MUST have the value
"application/tamp-apex-update".
The body of the message is the binary value of the DER encoding of
the TAMPApexUpdate, wrapped in a CMS body as described in Section 2.
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RFC 5934 TAMP August 2010C.6. Apex Trust Anchor Update Confirm Message
An HTTP-based Apex Trust Anchor Update Confirm message is composed of
the appropriate HTTP headers, followed by the binary value of the DER
encoding of the TAMPApexUpdateConfirm, wrapped in a CMS body as
described in Section 2.
The Content-Type header MUST have the value "application/
tamp-apex-update-confirm".
C.7. Community Update Message
A Community Update Message using the POST method is constructed as
follows: The Content-Type header MUST have the value "application/
tamp-community-update".
The body of the message is the binary value of the DER encoding of
the TAMPCommunityUpdate, wrapped in a CMS body as described in
Section 2.
C.8. Community Update Confirm Message
An HTTP-based Community Update Confirm message is composed of the
appropriate HTTP headers, followed by the binary value of the DER
encoding of the TAMPCommunityUpdateConfirm, wrapped in a CMS body as
described in Section 2.
The Content-Type header MUST have the value "application/
tamp-community-update-confirm".
C.9. Sequence Number Adjust Message
A Sequence Number Adjust Message using the POST method is constructed
as follows: The Content-Type header MUST have the value "application/
tamp-sequence-adjust".
The body of the message is the binary value of the DER encoding of
the SequenceNumberAdjust, wrapped in a CMS body as described in
Section 2.
C.10. Sequence Number Adjust Confirm Message
An HTTP-based Sequence Number Adjust Confirm message is composed of
the appropriate HTTP headers, followed by the binary value of the DER
encoding of the SequenceNumberAdjustConfirm, wrapped in a CMS body as
described in Section 2.
Housley, et al. Standards Track [Page 90]